Various means have been employed in the past to dispense particulate materials. These materials can be rather coarse, as in granular material, such as shingle granules. There is also a need to dispense finely divided particulate material, such as powders. Typical means for dispensing particulate materials include direct feed nozzles and open hoppers.
Some processes require a periodic starting and stopping of the dispensing process. For example, dispensing particulate material into continuously indexing containers, and depositing particulate material onto substrates in patterns.
Where there is a need for starting and stopping the dispensing of the particulate materials, a mechanical means, such as a fluted roll, is usually inserted at the bottom of the nozzle. Rotation of the fluted roll causes a predetermined amount of the particulate material to be dropped through the nozzle opening.
There is a need for a more accurate way to control the dispensing of particulate material, particularly where the dispensing is to be intermittent. As process speeds increase it becomes more and more difficult to precisely control the starting and stopping of the discharge of particulate material. Mechanical devices have been found to be deficient in accurately starting and stopping the process.
Lack of precise control in a process for depositing particulate material onto a substrate results in an imprecise or fuzzy boundary between the applied portion of the substrate and the non-applied portion of the substrate. Lack of precise control in a process for depositing particulate material into containers, compartmented receptacles or packages passing beneath the nozzle manifests itself in spillage of the particulate material outside the containers.
One cause of the impreciseness of typical particulate material depositing techniques is that the nozzles depend on gravity exclusively, not only for directing the particulate material from the nozzle, but also for movement of the particulate material within the nozzle itself. The use of gravity to move the particulate material within the nozzle, or discharge apparatus itself, has feed rate limitations, and there is no easy way to control the rate of flow of the particulate material.
An improved means and method for dispensing particulate material from a nozzle would eliminate the lack of preciseness inherent in the mechanical action of mechanically operated apparatus, such as a fluted roll. Also, the ideal system would provide a means for enhancing gravitational forces in starting and stopping flow and would enable some means for controlling the flow rate of particulate material during discharge.